Insight-HXMT observations of Swift J0243.6+6124: the evolution of RMS pulse fractions at super-Eddington luminosity

P J Wang,Y G Li,C M Zhang,X B Li,Y Zhang,C Z Liu,L Chen,J Zhang,S Zhang,X J Liu,G Q Liu,C K Li,Y B Chen,B Li,T X Chen,B S Liu,H M Zhang,W Z Zhang,Y Chen,X F Li,Z W Li,Z L Zhang,W S Wang,Y N Liu,G Chen,J Wang,T Zhang,W Zhang,Y F Zhang,G F Wang,Y S Wang,W C Zhang,X Li,Zhao Zhang,G Li,Zhi Zhang,S N Zhang,F Zhang,W Li,T P Li,Haiqiang Jia ,Bo Lü ,Wei Cui ,J L Qu ,M X Fu ,Jianfeng Zhou ,H S Zhao ,Ao Zhang ,Y Nang ,Bin Meng ,Xiaofan Zhao ,Chengcheng Guo ,Y Huang ,Meiling Li ,Yongwei Dong ,Xiang Ma ,Long Ji ,T Luo ,X F Lu ,Yuxuan Zhu ,J Y Nie ,Zhi Chang ,S M Jia ,C Cai ,Lian Tao ,G H Gao ,Yun-Cheng Yang ,Q Q Yin ,N Sai ,Yupeng Xu ,Yajiu Zhang ,Xiang-Yang Wen ,G C Xiao ,Fangjun Lu ,B B Wu ,Weiwei Cui ,Y Y Du ,Q Luo ,Shuo Xiao ,Hanwei Liu ,R C Shang ,Danxiang Han ,J Jin ,Q C Bu ,Y You ,J Y Liao ,Yi Yang ,Shi-Jie Zheng ,Y G Zheng ,Mei‐Hwan Wu ,Luhua Jiang ,Liming Song ,X H Liang ,You-Li Tuo ,G Ou ,J K Deng ,L J Wang ,J Guan ,X Y Song ,Y D Gu ,X L Cao ,Jiawei Yang ,Weichun Jiang ,He Gao ,Liang Sun ,Ying Tan ,Min Gao ,Yan Jin ,Q B Yi ,B Y Wu ,L D Kong ,Ming-Yu Ge ,D K Zhou ,S L Xiong ,Chunling Wang ,S Yang ,R L Zhuang

doi:10.1093/mnras/staa2448

Abstract

ABSTRACT Based on Insight-HXMT data, we report on the pulse fraction evolution during the 2017–2018 outburst of the newly discovered first Galactic ultraluminous X-ray (ULX) source Swift J0243.6+6124. The pulse fractions of 19 observation pairs selected in the rising and fading phases with similar luminosity are investigated. The results show a general trend of the pulse fraction increasing with luminosity and energy at supercritical luminosity. However, the relative strength of the pulsation between each pair evolves strongly with luminosity. The pulse fraction in the rising phase is larger at luminosity below 7.71 × 1038 erg s−1, but smaller at above. A transition luminosity is found to be energy independent. Such a phenomenon is first confirmed by Insight-HXMT observations and we speculate that it may have relation with the radiation-pressure-dominated accretion disc.

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